To get HD you must use a HDMI cable. We have this one and it works great and for the price you can't beat it. I hear though it wont work on Samsung TVs. Ours is a Sony Bravia.

Ummmm... I watch my Roku all the time on a Samsung TV

What you can't do with my model is stream Amazon videos direct (you can with all model years before and this year's, but not last years; both companies blame the other for the lack of "an app" that works).